U.S. Pat. No. 5,637,064 to Towley et al, which is assigned to the assignee of this invention, discloses an existing selectorized dumbbell that is known as the PowerBlock®. In this dumbbell, there are a plurality of nested weights each of which comprises a left weight plate and a right weight plate that are joined together by a pair of front and rear rails. The left and right weight plates of the nested weights are disposed in nested left and right weight plate stacks that are spaced apart from one another by the length of the front and rear rails. The rails of successive nested weights are longer and lower than the rails of the weight immediately to the inside to allow the weights to be nested together in the aforementioned manner.
The selectorized dumbbell disclosed in the 064 patent includes a handle that is dropped down into the gap between the left and right weight plate stacks. The handle has a pair of planar ends that are spaced apart from one another but are rigidly joined to one another at least by a central hand grip that extends between the ends and is affixed thereto. Each end of the handle includes a vertical array of substantially horizontally extending slots. The various slots in the array are vertically spaced from one another such that one slot is below each of the rails.
A weight selector comprising a U-shaped connecting pin having a pair of spaced, parallel connecting prongs is provided. The prongs of the connecting pin are insertable into the set of slots beneath the rails of a selected one of the nested weights. When the user then lifts the handle, the handle will carry with it the selected weight and all of the nested weights whose rails lie above the rail of the selected weight. Thus, the user can easily adjust the total weight carried by the handle, to adjust the exercise mass of the dumbbell, simply by repositioning the connecting pin from one set of slots to another.
The use of an insertable pin is an effective weight selector for a selectorized dumbbell. However, while it is unlikely to happen, it is possible for a user to incorrectly install the U-shaped connecting pin by inserting one connecting prong on one side of the pin beneath the rails of the selected weight and the other connecting prong on the other side of the pin beneath the rails of the weight either above or below the selected weight. This is called cross-pinning. Since the weights are not correctly held in their most stable configuration when they are cross-pinned, there is a small possibility of damage or failure of the connecting pin and consequent dislodgement of the weights from the handle. This is obviously a disadvantage.
In addition, prior connecting pins of the type described above have incorporated magnets that are magnetically attracted to the rail to which the cross member of the connecting pin is adjacent when the connecting pin is correctly installed in the set of slots beneath the rails of a selected one of the nested weights. This magnetic attraction is designed to be strong enough to form a magnetic latch that holds the connecting pin in place when the user is exercising with the dumbbell. However, the use of magnets increases the manufacturing cost of the connecting pin and increases the danger of disconnection in a cross-pinned situation since the cross member of the connecting pin no longer lies flush against a single rail. In addition, even when the connecting pin is correctly installed and the magnetic latch formed by the magnets is in place, very vigorous exercise in certain instances can very rarely overcome the magnetic attraction to cause the connecting pin to begin to detach from the handle. This is also obviously a disadvantage particularly when the dumbbell is being used in a setting, such as a fitness center or gym, where a particular user may not be intimately familiar with using selectorized dumbbells and correctly installing the connecting pin.
Accordingly, it would be an advance in the art for the weight selector of such a selectorized dumbbell to be designed in a way that would be very difficult for the user to cross-pin and that would have redundant features that would prevent inadvertent dislodgement. This would make selectorized dumbbells more attractive to multi-user exercise facilities, such as commercial fitness centers or gyms, as the proprietors of such facilities would not have to fear that their users would improperly use the dumbbells in ways that could potentially cause the weight selectors to inadvertently disengage during exercise activities.